1. Field of the Invention
This invention relates to the production of phenol and more particularly to a process for producing phenol and acetone from cumene hydroperoxide (CHP) using reactive distillation.
2. Description of the Prior Art
Phenol is an important organic chemical with a wide variety of industrial uses. It is used, for example, in the production of phenolic resins, bisphenol-A and caprolactam. A number of processes are currently in use for the production of phenol but the single process providing the largest proportion of the total production capacity is the cumene process which now accounts for over three quarters of the total U.S. production. The basic reaction involved in this process is the cleavage of cumene hydroperoxide into phenol and acetone:
C6H5C(CH3)2OOHxe2x95x90C6H5OH+(CH3)2CO 
The reaction takes place under acid conditions with the yield of both phenol and acetone generally being 40 percent or more.
On an industrial scale, the cumene hydroperoxide is usually treated with dilute sulphuric acid (0.5 to 25 percent concentration) at a temperature of about 50xc2x0 to 70xc2x0 C. After the cleavage is complete, the reaction mixture is separated and the oil layer distilled to obtain the phenol and acetone together with cumene, alpha-methylstyrene, acetophenone and tars. The cumene may be recycled for conversion to the hydroperoxide and subsequent cleavage. The phenol produced in this way is suitable for use in resins although further purification is required for a pharmaceutical grade product.
The heterogeneous cleavage of cumene hydroperoxide (CHP) over various solid acid catalysts has already been reported. For example, U.S. Pat. No. 4,490,565 discloses the use of zeolite beta in the cleavage of cumene hydroperoxide, whereas U.S. Pat. No. 4,490,566 discloses the use of a Constraint Index 1-12 zeolite, such as ZSM-5, and EP-A-492807 discloses the use of faujasite in the same process. The use of smectite clays in the acid-catalyzed decomposition of cumene hydroperoxide is described in U.S. Pat. No. 4,870,217.
U.S. Pat. No. 4,898,995 discloses a process for the coproduction of phenol and acetone by reacting cumene hydroperoxide over a heterogeneous catalyst consisting of either an ion exchange resin having sulfonic acid functionality or a heteropoly acid, such as 12-tungstophosphoric acid, on an inert support, such as silica, alumina, titania and zirconia. Such heteropoly acid catalysts are generally used as their hydrates, and as such are inherently unstable at temperatures in excess of 350xc2x0 C.
Catalytic distillation has been used to produce cumene by alkylating propylene with benzene. See, J. Shoemaker, et al., Cumene by Catalytic Distillation, Hydrocarbon Processing, p. 57, (June, 1987).
U.S. Pat. No. 4,935,577 to Huss, Jr., et al. discloses the use of Lewis acid promoted inorganic oxide catalyst systems for alkylation and oligomerization processes using catalytic distillation.
U.S. Pat. No. 5,055,627 to Smith, Jr., et al. discloses an alkylation process for preparing cumene from benzene and propylene in a zeolitic catalyst bed disposed in a distillation column reactor. The alkylated benzene is withdrawn from the distillation column reactor at a point below the fixed bed and unreacted organic aromatic compound may be taken off as an overhead.
U.S. Pat. No. 5,905,178 to Hildreth discloses a process for removing alpha-methyl styrene from admixtures with cumene by hydrogenation using catalytic distillation to selectively hydrogenate the side chains and produce cumene. The alpha-methyl styrene is produced as a byproduct in the cumene-phenol peroxidation process.
It is an object of the present invention to provide a process for the production of phenol and acetone using catalytic distillation. This process would provide a method of reacting cumene hydroperoxide which would avoid excessive heat buildup and utilize cumene hydroperoxide""s high heat of reaction (60.6 kcal/mol) to separate out low boiling point decomposition products, such as acetone.
The present invention relates to a process for producing phenol and acetone from cumene hydroperoxide, wherein the process comprises the steps of:
i) introducing a cumene hydroperoxide feed into a reactive distillation column comprising at its upper portion a distillation column and at its lower portion a catalyst bed, at a point above or at an upper portion of said catalyst bed;
ii) mixing a diluting portion of acetone with said cumene hydroperoxide to provide a diluted cumene hydroperoxide;
iii) directing said diluted cumene hydroperoxide through said catalyst bed under conditions sufficient to effect the exothermic decomposition of said cumene hydroperoxide to a product comprising a heavy fraction comprising and a vaporized light fraction comprising acetone;
iv) withdrawing said heavy fraction as bottoms from said column;
v) flowing said vaporized light fraction upwards through the catalyst bed and at least a portion of the reactive distillation column;
vi) condensing said light fraction to provide at least a portion of said diluting portion of acetone for subsequent mixing with said cumene hydroperoxide feed;
vii) optionally withdrawing a portion of said light fraction as overhead from said column; and
viii) repeating steps i) through vii).
Steps v) and vi) can be used to control dilution of the cumene hydroperoxide feed, e.g., by setting the reflux rate of acetone through said column. The liquid flow of the diluted cumene hydroperoxide through the reactor is preferably maintained at a rate sufficient to keep the catalyst bed wetted, thereby maintaining catalyst temperature at or near the boiling point of the liquid to provide isothermal operation of the process. Given that step vii) is optional, the presently claimed process includes operation under conditions of total reflux with all overhead product being returned to the column.
The diluting portion of acetone can be added to at least one of: 1) the upper portion of the distillation column, 2) the lower portion of the distillation column, upstream of said catalyst bed, e.g., at the CHP feed tray, and 3) the cumene hydroperoxide feed prior to its introduction to said distillation column. Recovered overhead which contains acetone can also be added directly at one or more locations to the catalyst bed in amounts sufficient to reduce formation of heavy compounds, i.e., compounds with normal boiling points greater than 182xc2x0 C., e.g., dimers of xcex1-methylstyrene (AMS). Such interstage injection of acetone diluent can be used to assist in maintaining the catalyst bed at a temperature at or near the boiling point of the reactant liquid to provide preferred isothermal operation, while eliminating reactor xe2x80x9chot spots.xe2x80x9d
In another aspect, the present invention relates to an apparatus for preparing phenol from cumene hydroperoxide which comprises:
a) a reactive distillation column comprising at its upper portion a distillation column and its lower portion a catalyst bed;
b) a lower outlet downstream of the catalyst bed for removing high boiling bottom products comprising phenol;
c) an inlet at or near the bottom of said distillation column for introducing cumene hydroperoxide feed at a point upstream of said catalyst bed;
d) an upper outlet for removing low boiling overhead products comprising acetone;
e) a heat exchanger upstream of said upper outlet for cooling said overhead products;
f) an overhead products receiver upstream of said heat exchanger having an outlet from which said overhead products are collected and/or returned to said distillation column; and
g) overhead products inlet at an upper portion of said distillation column for introducing overhead products reflux from said receiver.
The apparatus can further comprise an element selected from the group consisting of
h) an overhead products inlet at a lower portion of said distillation column for introducing overhead products from said receiver to said distillation column at or near said inlet for introducing cumene hydroperoxide;
i) an overhead products line which recycles overhead products to the cumene hydroperoxide feed upstream of said inlet for introducing cumene hydroperoxide; and
j) an overhead products line which recycles overhead products to one or more portions of the catalyst bed.
The process and apparatus of the invention can achieve at or near 100% conversion of cumene hydroperoxide at long on-stream times with high selectivity to phenol and acetone and with extremely low coproduction of high boiling impurities such as 4-cumylphenol, and 2,4-diphenyl-4-methyl-1-pentene. Moreover, the present invention allows efficient use of the heat of reaction evolved from decomposition of cumene hydroperoxide to effect separation of lower boiling products, e.g, acetone, from the reaction product mixture. Such an arrangement minimizes reboiler use, reducing energy costs, while providing higher yields, good product purity and lower capital investment.